1. Field of the Invention
The present invention relates to a brake system for vehicles such as automobiles, and more particularly, to a brake system for vehicles which comprises braking force generation means adapted to generate braking forces according to the amount of depression of a brake pedal.
2. Description of the Prior Art
The brake system for vehicles such as automobiles generally comprises braking force generation means provided for each of the wheels, each including a rotary member such as a brake rotor or a brake drum constructed to rotate together with a corresponding wheel and a movable member such as a brake pad or a brake shoe constructed to be driven according to the amount of depression (force or stroke of depression) of the brake pedal, so that each of the braking force generation means generates a braking force by a friction material of the movable member being pressed against the rotary member, so as thereby to brake the rotation of the corresponding wheel.
As one of those brake systems there is known an electric brake system in which the movable member of the braking force generation means is driven by an ultrasonic motor, wherein the ultrasonic motor provided for each of the wheels is controlled according to the amount of depression of the brake pedal, while the braking force generation means is constructed to dissolve a braking force generating condition when it went wrong in a condition of generating a braking force.
According to such an electric brake system of the prior application, since the ultrasonic motors are controlled separately for each of the wheels, the braking force of each of the wheels can be controlled independently of those of other wheels, and since the braking condition is dissolved even when the braking force generation means went wrong in a condition of generating a braking force, there can be avoided such a trouble that the running of the vehicle is interfered by a standing generation of a needless braking force due to a trouble of the brake system.
However, in the above-mentioned conventional electric brake system, although a fail-safe is cared for against a trouble of each of the braking force generation means each provided for each of the wheels, the stability of the behavior of the vehicle under a condition that the braking force generation means of a certain one of the wheels went wrong, i.e., the running stability of the vehicle as a whole, leaves a large room for further improvements.
In more detail, if the braking force generation means of either one of the wheels went wrong, there occurs a situation during a braking of the vehicle that, while the braking force of the wheel where the braking force generation means went wrong makes no change in spite of any change of the amount of depression of the brake pedal, the braking force of the wheel transversely opposite to the wheel where the braking force generation means went wrong changes according to the amount of depression of the brake pedal (an unbalanced braking condition), whereby a needless yaw moment is applied to the vehicle, deteriorating the running stability of the vehicle. Such a problem is latent not only in the electric brake system but also in various types of brake systems by which the braking of each of the wheels is controllable independently of those of the other wheels by each braking force generation means provided exclusively for each corresponding wheel.
Particularly when the braking force generation means went wrong to generate no braking force, a needless yaw moment is applied to the vehicle according to the depression of the brake pedal by a driver, rendering the vehicle to be liable to a deterioration of behavior, while on the other hand, if the braking force generation means went wrong to hold a braking force, the vehicle is subjected to a fluctuating yaw moment according to a depression of the brake pedal by the driver, thereby causing not only a deterioration of the running behavior of the vehicle but also causing a useless consumption of the kinetic energy generated by the engine for driving the vehicle. The adverse effect of a trouble occurred in the braking force generation means on a deterioration of the behavior of the vehicle is generally more noticeable when the engine is generating a higher level of kinetic energy, i.e. the vehicle speed, and therefore the momentum of the vehicle, is higher.
The present invention was made in view of the above-mentioned problems in conventional brake systems such as the electric brake system which are capable of controlling the braking force of each of the wheels independently of those of other wheels. A primary object of the present invention is to improve the running stability of vehicles than ever, by preventing a needless too large yaw moment from being applied to the vehicle when the braking force generation means of either one of the wheels went wrong, so as thereby to decrease or eliminate any adverse effect being applied to the vehicle due to the trouble of the braking force generation means.
According to the present invention, the above-mentioned primary object is accomplished by a brake system for vehicles, comprising braking force generation means each provided for each of wheels to generate a braking force according to an amount of depression of a brake pedal, and control means for controlling each of the braking force generation means for each of the wheels independently of the other braking force generation means for the other wheels, wherein when either one of the braking force generation means went wrong, the control means controls other normal one or ones of the braking force generation means, so as substantially not to apply any needless yaw moment to the vehicle.
According to the above-mentioned construction, when either one of the braking force generation means went wrong, the control means controls other normal one of ones of the braking force generation means so as substantially not to apply any needless yaw moment to the vehicle, whereby it is definitely prevented that there occurs such a situation that the vehicle is applied with a needless excessive yaw moment during a running thereof.
Alternatively, according to the present invention, the above-mentioned object is accomplished by a brake system for vehicles, comprising braking force generation means each provided for each of wheels to generate a braking force according to an amount of depression of a brake pedal, and a control means for controlling each of the braking force generation means for each of the wheels independently of the other braking force generation means for the other wheels, wherein the vehicle has an engine for generating a kinetic energy for the vehicle to run, and when either one of the braking force generation means went wrong, the control means restricts the generation of the kinetic energy by the engine.
According to the above-mentioned construction, when either one of the braking force generation means went wrong, the generation of the kinetic energy by the engine is restricted, whereby it is suppressed that the speed and the kinetic energy of the vehicle rise high, so that thereby an adverse influence of a needless yaw moment being applied to the vehicle due to a malfunction of the braking force generation means on a stable running of the vehicle is decreased.
In the above-mentioned construction, when either one of the braking force generation means went wrong to generate substantially no braking force, the control means may forbid one of the braking force generation means positioned transversely opposite to the wrong braking force generation means to operate, so as to prevent a needless yaw moment from being applied to the vehicle. According to such a construction, it is definitely avoided that there occurs an unbalance braking condition such that the wrong braking force generation means generates no braking force during a braking of the vehicle, while the braking force of one of the braking force generation means positioned transversely opposite to the wrong braking force generation means changes according to the amount of depression of the brake pedal, so as thereby to apply a needless yaw moment to the vehicle.
In the above-mentioned construction, when either one of the braking force generation means went wrong not to substantially release a generated braking force, the control means may operate one of the braking force generation means positioned transversely opposite to the wrong braking force generation means to generate a braking force, so as to prevent a needless yaw moment from being applied to the vehicle.
In the above-mentioned construction, when either one of the braking force generation means went wrong not to substantially release a generated braking force, the control means may operate one of the braking force generation means positioned transversely opposite to the wrong braking force generation means to generate a braking force, so as to prevent a needless yaw moment from being applied to the vehicle. According to such a construction, it is definitely prevented that the behavior of the vehicle is abruptly deteriorated.
In the above-mentioned construction, the control means may comprise means for calculating a target yaw moment for the vehicle according to a running condition of the vehicle, and when either one of the braking force generation means went wrong, the control means may control other normal one or ones of the braking force generation means, so that the yaw moment of the vehicle substantially coincides with the target yaw moment. According to such a construction, it is possible to protect the behavior of the vehicle from being deteriorated by a malfunction of one of the braking force generation means, while ensuring a good turning performance of the vehicle.
In the above-mentioned construction, when either one of the braking force generation means went wrong to generate substantially no braking force, the control means may control other normal ones of the braking force generation means, so that the braking force generated by one of the braking force generation means positioned longitudinally opposite to the wrong braking force generation means substantially coincides with the sum of the braking forces generated by front and rear ones of the braking force generation means positioned on a side transversely opposite to a side of the wrong braking force generation means. According to such a construction, it is definitely prevented that there occurs such a situation that there is generated a large difference between the sum of the braking forces generated by front and rear ones of the braking force generation means positioned on one side of the vehicle and the sum of the braking forces generated by front and rear ones of the braking force generation means positioned on the other side of the vehicle according to an amount of depression of the brake pedal.
In the above-mentioned construction, the vehicle may have an engine for generating a kinetic energy for the vehicle to run, and when either one of the braking force generation means went wrong not to substantially release a generated braking force, the control means may operate one of the braking force generation means positioned transversely opposite to the wrong braking force generation means to generate a braking force, so as to prevent a needless yaw moment from being applied to the vehicle, while the control means may restrict the generation of the kinetic energy by the engine. According to such a construction, an adverse influence of the malfunction of the braking force generation means on the behavior of the vehicle is decreased, whereby a deterioration of the behavior of the vehicle is effectively prevented as compared with a case where the generation of the kinetic energy by the engine is not restricted, while it is made possible to save such a kinetic energy that would be generated by the engine but uselessly consumed by the braking.
In the above-mentioned construction, the braking force generation means may constructed as an electric braking force generation means using an electric motor as an actuator.
In the above-mentioned construction, it may be judged if there is any allowance for increase in the braking force available by one of the braking force generation means positioned longitudinally opposite to the wrong braking force generation means, and when there is no allowance in the available braking force, the target braking force for one of the braking force generation means positioned longitudinally opposite to the wrong braking force generation means may be set to the available braking force, so that the target braking forces for other wheels are set according to the available braking force.
In the above-mentioned construction, when either one of the braking force generation means went wrong not to substantially release a generated braking force, when the vehicle is running straight forward, the target braking force of one of the braking force generation means positioned transversely opposite to the wrong braking force generation means may be set to be substantially equal to the braking force generated by the wrong generation means, while when the vehicle is substantially turning, the target braking force of one of the braking force generation means positioned diagonally opposite to the wrong braking force generation means may be set to be substantially equal to the braking force generated by the wrong braking force generation means.
In the above-mentioned construction, the control means may be constructed to calculate the target braking force of one of the braking force generation means positioned longitudinally opposite to the wrong braking force generation means according to an amount of depression of the braking pedal, and to calculate the target braking forces of front and rear ones of the braking force generation means on a side transversely opposite to the side of the wrong braking force generation means so that the sum thereof is substantially equal to the target braking force of the above-mentioned one braking force generation means, so as thereby to control the braking forces of all of the braking force generation means, except the wrong braking force generation means, to correspond to the target braking forces respectively corresponding thereto.
In the above-mentioned construction, the target braking forces of the above-mentioned front and rear ones of the braking force generation means may be calculated so that the target value for the front braking force generation means is greater than that for the rear braking force generation means.
In the above-mentioned construction, the vehicle may have an engine for generating a kinetic energy for the vehicle to run, and when either second one of the braking force generation means went wrong with either first one of the braking force generation means having gone wrong, the control means may decrease the generation of the kinetic energy by the engine.
In the above-mentioned construction, when either two front ones or two rear ones of the braking force generation means went wrong, the control means may restrict the generation of the kinetic energy by the engine, while when either front and rear right ones of the braking force generation means or front and rear left ones of the braking force generation means went wrong, the control means may gradually decrease the generation of the kinetic energy by the engine.